Tag Archives: IR

Following up on Part 1, it’s time to talk about the “brains of the operation”. Bare with me, this is going to be a rather long read.Hardware selection

The DAC needed to be controlled by a microcontroller so I looked into my options. I wanted something that would:

Be easy to program, so the Arduino IDE was a must.

Be able to drive a TFT.

Have enough storage capacity to store enough code & fonts for the TFT.

Be readily available.

Be relatively low cost, since it would have no influence on the dac’s SQ.

Be easy to build / integrate into a new design, even by a novice.

After some consideration, I decided to use an STM32F103 ready-made module. It would plug in to a “mainboard” of my design, along with the chosen TFT. It would be fast enough, have enough flash & ram, be easy to integrate and develop for and it would cost next to nothing.

Next up was the TFT. I’d seen on Ebay an interesting one that was relatively big, high resolution and inexpensive. It was this one:

It can be found on Ebay by searching for “3.5 tft uno 320 x 480”. Expect to pay 6-8€ inc. shipping.

After some searching I found a suitable library that (after some slight tinkering) would allow my tiny STM32 to drive it properly. (Note: do not download the library from this link. I will provide a customized version of the library together with my code).

I found a ready-made library for configuring the Si570 and modified it to run on my STM32, using one of its hardware I2C ports. I will also include this library in my code. To complete the recipe I also found working rotary encoder and IR receiver libraries.

The code

Next up was the prototyping work. I adapted my TFT HiFiDuino Pro code to run on the STM32 & TFT combo, with support for AK4490 dual mono operation. The end result had this feature list:

Support for either Dual Mono or single chip setups.

Support for the Amanero Combo384 USB to I2S module (must be set up as slave with MCLK/2 and F0,1,2,3 enabled).

Control with one rotary encoder with push-to-select functionality.

IR Remote support.

Support for software volume control, from -99dB to 0dB

Display incoming signal sampling rate and type, determined by “reading” the relevant I/O pins of the USB to I2S board.

Display and control of the AK4490’s digital filter.

Selection of the proper MCLK frequency according to incoming SR and type and programming of the Si570 accordingly.

Control of “DSD Direct” function of the AK4490s.

Control of the DSD Filter’s Frequency (50KHz or 150KHz).

Control of the Sound Mode of the AK4490.

Choice of either inverted or normal analog output for the AK4490s.

Choice of two sets of MCLK frequencies, either 22/24MHz or 45/49MHz.

Remote power on/off functionality (or always on – configurable in the code).

IR remote library, compatible with the SMT32 (modified version of this library also included in the ZIP)

In the download I am including the modified versions of the libraries (as mentioned above) as well as the necessary font files. Be sure to extract the contents of “Libraries (place in Libraries folder)” to your Arduino IDE’s “libraries” folder.

Compatible IR remote control (Apple Remote or other – in any case you must edit the code and input the proper IR codes for your remote, see below)

STM32 TFT Motherboard Bill of Materials

PCB Part

Value

Notes

C1, C2, C3, C4, C5, C6, C7, C10, C11

100n, 0805

D1

1N4001, DO214BA

L2

Ferrite bead, low R, 1206/3216

LED1, LED2

LED 1206

Q1

AO3400, SOT23

Q2

BC808, SOT23

R1, R2, R3, R4, R12, R13

2.2 – 3.3Κ, 0805

R5, R7

2.2K, 0805

R6

5.1K, 0805

R8, R11

1K, 0805

R9, R10

10K, 0805

U1

24LC256, SO-08

U2, U4

SI8605, SOIC-16

U3, U5

MCP23008, SO-18W

DC_5V

.100 (2.54mm) – 2 Pin

EXP

.100 (2.54mm) – 2×4 Pin

I2C

.100 (2.54mm) – 3 Pin

I2C_ISOL1A, I2C_ISOL1B

.100 (2.54mm) – 6 Pin

I2C_ISOL2

.100 (2.54mm) – 3 Pin

IR

.100 (2.54mm) – 3 Pin

JP1, JP2

.100 (2.54mm) female – 6 Pin

JP3, JP4

.100 (2.54mm) female – 8 Pin

UART

.100 (2.54mm) – 3 Pin

MCP_ISOL1

.100 (2.54mm) – 10 Pin

MCP_ISOL2

.100 (2.54mm) – 2×6 Pin

POWER_RELAY

.100 (2.54mm) – 2 Pin

ROTENC

.100 (2.54mm) – 4 Pin

STM32_BLUE_PILL

STM32F103C uC board

How do I make it work?

Power

You have to supply the board with 5VDC at ~300mA through header DC_5V.

DC_5V

Pin

Function

+

5VDC

-

GND

Basic connectivity

Serial port:

UART

Pin No.

Function

1

RXD (PA10)

2

TXD (PA9)

3

GND

Rotary encoder:

ROTENC

Pin No.

Function

1

PB13

2

PB14

3

PB15

4

GND

IR control:

IR

Pin No.

Function

1

PB9

2

GND

3

Vcc

If you will be controlling a power on/off relay, you can use the POWER_RELAY header:

POWER_RELAY

Pin

Function

+

5VDC

-

GND

Expansion header:

EXP

Pin No.

Function

1

3.3V

2

GND

3

PB3

4

PA8

5

PA15

6

PB1

7

PA12

8

PB0

I2C header (non-isolated):

I2C

Pin No.

Function

1

GND

2

SCL (PB10)

3

SDA (PB11)

Isolated I2C ports

The board has provisions for two separately isolated I2C ports, complete with I/O expanders on their isolated sides. The idea is to connect the DAC board to one of the isolated ports (I2C_ISOL1 & MCP_ISOL1) and your USB-to-I2S board to the other isolated port (usually MCP_ISOL2)